Manufactured tobacco and smoking articles are well-known. See, e.g., U.S. Pat. Nos. 235,885; 235,886; 2,433,877; 2,445,338; 2,485,670; 2,592,553; 2,598,680; 2,845,933; 3,012,562; 3,085,580; 3,098,492; 3,141,462; 3,203,432; 3,209,763; 3,223,090; 3,298,062; 3,313,003; 3,353,541; 3,364,935; 3,373,751; 3,404,690; 3,404,691; 3,410,279; 3,467,109; 3,528,434; 3,529,602; 3,760,815; 3,894,544; 3,931,824; 3,932,081; 4,083,371; 4,233,993; 4,333,484; 4,340,072; 4,347,855; 4,391,285; Re. 24,424; U.S. Defensive Publication No. T912,011; German Publication Nos. 1,167,717, 1,532,104, 1,782,854, 2,358,657, 2,410,168, and 2,633,627; Canadian Patent No. 951,209; U.K. Publication Nos. 282,369 and 2,064,296; Swiss Patent No. 275,420; Belgian Publication No. 828503; South African Publication No. 69/838; Netherlands Publication No. 143,799; and commonly assigned U.S. Pat. No. 4,510,950, issued Apr. 16, 1985. Some of those documents refer to casting or extrusion of sheets, strands or filaments of tobacco-containing materials or to extrusion of tobacco rods containing axially directed air channels. Some of the products are expanded, foamed, or both.
One approach to making a foamed, extruded smoking article is disclosed in commonly assigned U.S. Pat. Nos. 4,510,950 and 4,625,737 and 4,632,131 the disclosures of which are incorporated by reference in their entirety. The smoking article is typically substantially cylindrical and is extruded under conditions such that the water in the wet blend fed to the extruder die is converted to steam, thereby foaming the article. The article is monolithic, that is, it is extruded as a single strand with a diameter of from about 2 to about 35 mm, preferably from about 4 to about 25 mm, typically about 4 to 8 mm if the article is a cigarette.
Another approach is to extrude the wet blend out a die having a plurality of small apertures to form an extruded, coherent, multistrand, tobacco-containing, generally cylindrical smoking article comprising a plurality of co-extruded strands that extend generally along the longitude of the smoking article and are adhered to one another, preferably randomly, so as to leave flow passageways between the strands along the longitude of the smoking article. This approach is disclosed in commonly assigned U.S. Pat. No. 4,632,131. The configuration of the strands and passageways of these foamed articles provide sufficient heat transfer area or sufficient residence time or both for the hot gases drawn towards the proximal end of the smoking article by a smoker to cool and to exit the proximal end at a temperature comfortable for the smoker.
Extruded tobacco materials, particularly the foamed, extruded tobacco materials discussed in U.S. Pat. Nos. 4,625,737 and 4,632,131, are formed from tobacco particles, binder, water, and optionally fillers or other desired additives. They are generally hot, moist, soft, and flexible thermoplastic-like materials as they exit the die. The temperature of the extruded materials is typically in the range from 40.degree.-150.degree. C. Working the tobacco-containing material at too high a temperature can result in overworking or cooking of the material, which degrades the quality of the product. Extruding the material at too low a temperature will not foam the material at typical extruder pressures, resulting in too dense a product. The moisture content, measured in terms of oven volatiles or OV, is typically in a range from 15 to 50%, depending on the product formulation and process conditions. This moisture content is above the tobacco equilibrium content of about 10-15%. The terms "moisture content" or OV refers to the solvent in which the tobacco and other materials are mixed before extrusion. Typically, the solvent is water, but organic or alcoholic solvents may be used.
Such continuously formed foamed rod-like extruded materials are too hot, moist, and pliable to be formed directly into smoking articles at high rates of speed by, for example, passing the rods into an automated smoking article "maker" machine such as a Mark 8 Cigarette Maker manufactured by the Molins Company or the like. These materials do not have enough structural integrity to be wrapped and formed into smoking articles without further processing.
The known methods of post extrusion processing of extruded materials include drying the extruded materials to reduce the OV to about the equilibrium OV of tobacco. Drying occurs commonly by allowing the solvent used in the pre-extruded slurry, e.g., water or other agents such as alcohols that aid in evaporation, to evaporate in air at atmospheric or reduced pressures. In some cases suction devices may be used to remove the solvent before drying. In other cases, the extruded materials are dried by infra-red heaters, steam, or hot air, in a conventional drying oven.
The foregoing techniques are inadequate for commercial utilization of continuously extruded materials, particularly foamed extruded materials, because they require long periods of time to reduce the OV to the desired level. These techniques require storage facilities or drying ovens (which can extend hundreds of feet) to sufficiently dry the material, each of which are impractical and costly to maintain in a commercial operation. With very slow rates of drying or low temperature drying, a foamed structure can collapse under its own weight, develop undesirable flat spots against a supporting structure, or otherwise result in a product having a non-uniform density. This adversely affects the burn qualities and consumer acceptance of the smoking article. Attempts to heat rapidly the materials, particularly foamed rods, result in case hardening the outer portions of the extruded material, which in turn inhibits the interior section from drying sufficiently. Case hardening can increase the drying time by an order of magnitude, e.g., from minutes to hours, or hours to days. Over-drying the exterior to dry the interior can result in a brittle product that crumbles when manipulated. Over-drying also can lead to a wrinkled or cracked product or an unduly stiff product, each of which is unacceptable to the consumer.
It also is known to use microwave energy to dry extruded materials somewhat uniformly to reduce the OV to the desired level. However, known microwave drying techniques do not adequately solve the space and time requirements needed to dry continuously advanced foamed, extruded tobacco-containing material into smoking article forming apparatus at high rates of speed in a commercially feasible operation. Moreover, even with known microwave drying, the extruded materials are still too pliable to be formed into the desired smoking article.
Among the objects of the present invention are:
to provide an improved method and apparatus for post extrusion processing of an extruded tobacco-containing material;
to provide a method and apparatus for rapidly processing a continuously advancing, tobacco-containing, foamed, extruded rod-like product for use in apparatus for forming smoking articles at high rate of speed;
to provide a method and apparatus for producing foamed, extruded tobacco-containing smoking articles having a substantially uniform density characteristic;
to provide a method and apparatus for producing extruded, tobacco-containing smoking articles having a uniform circumference, length, moisture content; and
to provide a method and apparatus for producing extruded tobacco-containing smoking articles where the solubles are substantially inhibited from migrating to the surface of the articles; and
to provide a method and apparatus for producing foamed extruded tobacco containing smoking articles having applied thereto a solid and preferably a powdery material for modifying the characteristics of the extruded material.